Field of the Invention
Aspects of the present invention relate to systems and methods for non-invasively measuring physical properties of materials in a conduit and for measuring physical properties associated with materials flowing through a conduit.
Discussion of Related Art
The measurement of one or more physical properties of immobile or flowing materials is an indispensable part of many technological processes spanning a wide variety of industries that include, for example, chemical, pharmaceutical, petro and oil, food, building materials, and waste water. Density, viscosity, volumetric flow rate, and mass flow rate are physical properties of free-flowing materials that are considered challenging for non-invasive measurement. As used herein, the term free-flowing material refers to liquids, loose solids, and their combination, e.g., slurries.
Non-invasive measurement of the physical properties of materials within a confined area has been conventionally performed by inspecting the material using one of several approaches. The inspection techniques employed may be radiometric, gravitational, electromagnetic, optical or ultrasound-based in nature. Radiation-based methods monitor attenuation of radioactive energy passing through a container's walls and the material contained within. Unfortunately, radiation-based methods suffer from a number of disadvantages. For instance, density is typically a prime focus of such methods because radiation-based methods are generally not applicable to measurement of shear resistance-relating variables such as viscosity of liquids, coalescence of solid particles, or material flow rates. Further, acquiring a license for the use of portable radiation-based density measurement devices may be burdensome and time consuming in certain jurisdictions and may require certified personnel to be trained and certified. Moreover, these systems may perform with reduced accuracy for certain density ranges, such as those associated with light powder materials in the range from 20 to 150 g/L. Additionally, radiation-based systems may require special design and operational effort to maintain a sufficient degree of safety and security.
Gravitational systems for measuring the density of non-gaseous materials require adjustment to account for the empty vessel's weight and internal dimensions. Gravitation systems are limited in their applicability due to the problems with installation of the weight-measuring equipment which frequently utilize various load cell arrangements. In addition, weight-measuring systems are not applicable to viscosity measurement.
Optical methods are applicable to measuring density of materials in vessels equipped with an aperture for focusing an optical beam through the filling material. Optical, non-invasive methods for density measurement may have limited use due to transparency requirements placed on the material to be measured.
The propagation of ultrasound waves through a material may also be used to measure one or more physical properties of materials. Ultrasound-based methods demonstrate the ability to discriminate between various physical properties of the material. If applied to liquids, these methods allow measurement of density or viscosity. However, conventional measuring methods that utilize ultrasound waves suffer from several disadvantages.
For example, ultrasound-based methods require a substantial amount of homogeneity of the filling material when used for density or viscosity measurements. Thus, ultrasound-based technologies are not applicable to loose solids and heterogeneous liquids like mud, suspensions, pulp or slurry. The presence in a vessel of various kinds of agitating members, mixers or bubblers can produce a similar effect on the accuracy of density or viscosity measurement. In addition, these methods require an ultrasound emitter/receiver attachment to the vessel wall. These attachments may require special treatment of the container's surface in order to create a conduit for ultrasound waves emitting by a transducer into the container. Moreover, ultrasound-based methods are highly sensitive to disturbances affecting the speed of sound in the medium, e.g., temperature and flow variations. Thus, special compensation techniques are conventionally employed to provide for the invariance of the output variables to these disturbances. Also, the amount of power consumed by an ultrasound transducer in providing a sufficient pulsation could limit the applicability of these methods.
The measurement of other physical properties, including flow rates such as volumetric and mass flow rates, of a material may be performed by a wide variety of devices. For example, coriolis meters may measure the mass and volumetric flow rate of a material and vortex flow meters may measure the volumetric flow. Some devices may utilize an invasive technique for determining flow rates, such as mechanical devices that include a rotating member for measuring the speed of the moving material. Other devices may utilize a non-invasive technique for determining flow rates, such as volumetric flow meters that use the Doppler Effect of ultrasound waves, or flow meters that utilize ultrasound waves generated by the friction between moving material and the inner surface of the pipe.